The present invention relates generally to steering systems, and more particularly, to torque-based steering control for steer-by-wire vehicles.
Steer-by-wire (SBW) systems altered traditional automotive steering systems by eliminating two mechanical connections. In traditional steering systems, the steering column is mechanically attached to a steering shaft. Similarly, the steering shaft is mechanically attached to a rack and pinion. SBW systems eliminate these two mechanical connections and replace them with electrical connections. In addition, electronic components and systems are added to the steering column and the rack and pinion to allow the system to function and to enable communication between steering components.
Currently, in the event of a steering system failure, such as when a mechanical blockage prevents the steering wheel from turning, the driver does not have any means of directing the vehicle. The loss of vehicle control can lead to undesirable consequences. Because only one method for steering control currently exists on known SBW systems, an alternate method is needed which provides the driver with adequate vehicular control in the event of a steering system failure. The present invention is directed to meeting this end.
One object of the invention is to provide a reliable means to steer a vehicle equipped with a steer-by-wire (SBW) system in the event of a steering system malfunction. Another object of the invention is to provide an alternative method to change the direction of travel of any vehicle.
In one aspect of the invention, a torque-based method to steer a vehicle equipped with a SBW system begins when a driver applies torque to a steering wheel so as to change the direction in which the vehicle travels. Two sensors, a steering wheel angle sensor and a steering wheel torque sensor then generate an angle signal and a torque signal, respectively. When the vehicle steering system is operating normally, the angle signal is used to generate a reference signal. The reference signal is then modified and used to move the road wheels to a position corresponding to the signal.
However, in the unlikely event that the vehicle steering system malfunctions, the steering wheel could become locked. In this case, an angle signal cannot be generated because the steering wheel angle measures the difference in position of the steering wheel itself. However, if the driver continues to apply torque to the steering wheel, the steering wheel torque sensor will still generate a torque signal. This torque signal then is used in place of the angle signal to generate the reference signal. Once the reference signal is generated, then it can be used to generate the road wheel angle signal, which is in turn used to position the road wheels accordingly.
The present invention thus achieves an alternative method to steer vehicles equipped with SBW systems. The present invention is advantageous because it provides a reliable method to steer a vehicle in the event of a steering system malfunction.
Additional advantages and features of the present invention will become apparent from the description that follows and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.